The present invention generally relates to surface inspection and review systems and methods. In particular, the present invention relates to improved system and method for detecting and analyzing anomalies on surfaces such as surfaces of silicon wafers.
Surface inspection systems are widely used in the semiconductor manufacturing industry to inspect the surfaces of various material wafers to monitor and detect defects. These systems are typically based on an imaging method, a light scattering method, or a combination of both.
In the imaging method, the surface of a wafer under test is imaged (using an image sensor array) and the image analyzed. In general, imaging based inspection systems have higher sensitivity in inspecting patterned wafers compared to sensitivity of light scattering method based systems for patterned wafers.
In the light scattering method, light is introduced to the surface of a wafer under test and scattered light is captured and analyzed. In general, light scattering based inspection systems have higher sensitivity in inspecting unpatterned wafers compared to sensitivity of imaging method systems for unpatterned wafers.
Conventionally, imaging based systems have lower throughput than that of the light scattering based systems, and therefore are used to inspect wafers only on a sampling basis. Accordingly, it takes a relatively long time to image the entire wafer surface. It would be preferable to inspect all patterned wafers rather than inspecting merely a sampling of the wafers.
To increase the throughput of the inspection systems for inspecting patterned wafer surfaces, several approaches were proposed and implemented. In particular, efforts have been made to develop a light scattering based system that is optimized for both patterned and unpatterned wafer inspection.
However, each of these prior art systems presents its own set of shortcomings. For example, many prior art systems lack the polar and azimuthal angular resolution of the scattered signal. Without the angular resolution of the scattered signals, not only is it difficult to identify defects, but also difficult to categorize or classify defects if and when identified. Other prior art systems include many optical elements in complex configurations that lead to attenuation of collected scattering signals. With attenuated signals, it is difficult to identify defects. Yet other prior art systems use ellipsoidal mirrors to collect scattering light and to direct them to fibers or detectors. Such systems are overly sensitive to misalignments, present alignment and focusing challenges, and provides distorted scatter signal angular information due to the ellipsoidal mirrors.
Accordingly, there remains a need for a system and method that alleviates or overcomes these shortcomings.